Yeah, around here, 250 Superbike is really popular. Hopped-up 250s and stock 300s. Adding restricted 400s may make it even more fun! The 400 seems to be stuck in between though. Too much for 250/300 classes, etc. not strong enough for the 450 Superbike (600 Supersport bikes with 1 cylinder disabled). There's a lot of overlap with Formula-II and F-III as well. So confusing, I'm still trying to sort it out!